High-frequency electron discharge device



Jan# .8, 1952 D. R. HAMILTON 2,581,408

LIGH-FREQUENCY ELECTRON DISCHARGE DEVICE Filed April 16, 1947 TTORNEY Patented Jan. 8, 1952 ECE HIGH-FREQUENCY ELECTRON DISCHARGE DEVICE Donald It. Hamilton, Princeton, N.v J., assignor to The Sperry Corporation, acorporation of Delar.

Ware

ApplicationAprii 1,6, 1947, Serial No. 741,895

16 Claims- 1 The present invention relates to the art including ultra-high-frequency electron discharge de vices utilizing cavity resonatorsy as frequency-determining elements thereof. In one aspect, it is more particularly directed to such electron discharge devices utilizing secondary emissive electrodes for increasing the power output of s uoh tubes.

TheA present invention is particularly applicable to the single cavity resonator electron discharge device known as a reex Klystron and shown in Fig'. 2 of U. S. PatentNo. 2,250,511 for Oscillator Stabilization System, granted July 29, 1941.

Areiiex Klystron comprises a. cathode, a cavity resonator havingA a pair ofv electron-permeable walls aligned with the cathode, and a reflector or repeller electrode beyond the cavity resonator. Incperation, the electron beam from the cathode is velocity modulated by the oscillating electromagnetic field within the resonator to become density modulated in the bunchingV space between the cavity resonator and reflector, and is redirected through the resonator to give .up energy tothe field and sustain its oscillations.

It is an object of the present invention to provide an improved cavity resonator ultra-highlfrequency electron discharge device utilizing a secondary-.emissive electrode.

It is another object of the presentinvention to provide an improved reflex Klystron capable of producing large power output.

It is still another object of the present invention to provide a novel single resonatorelectron discharge device in which secondary cathodes are disposed on both sides of the resonator,

It is yet another object of the present invention to provide a novel cavity resonator electron-discharge device in which the necessity ofL a continuously operating primary cathode is obviated.

The invention also relates tothe novel features or principles of the instrumentalities described herein, whether or not such are used for the stated objects, or in the stated elds or combinations.

In accordance with one aspect of the invention, secondary-ernissive grid structure is provided intermediate the resonator and the refiector of a reiiex K ystron, whereby the redirected4 densitylnodulated beam impnges upon the secondaryeniissive grid structure and produces a densitymodulated secondary beam of greater power: The enhanced beam produces a greater power output from the reex Klystrcn. In a preferred embodiment, the secondary-emissive grid structure is biased and positioned with respect to the 2 resonator to minimize the transit time of the density-modulated secondary beam between the grid andthe resonator whereby the debunching of the density-modulated secondary beam is minimized,

In accordance with another aspect of the invention, there is provided an electron discharge device having a single cavity resonator in which there are' electron-permeable openings in opposing walls; a secondary-emissive grid structure disposed on each side of the cavity resonator and aligned with the electron-permeable openings; and a reflector beyond each secondary-emissive grid and also aligned with said openings. With proper choice of operating potentials on the various elements of the device, a self-sustaining oscillator results, thereby eliminating the necessity of providing a primary source of electrons during operation.

In the drawings,

Fig. 1 is an elevation view, partly inl section, of an improved reflex Klystron in which a secondary-emissive grid is positioned between the resonator and the reflector, together with a schematic circuit diagramA for such Klystr-on;

Fig. 1A is an enlarged fragmentaryvievr in section, showing the secondary-emissive grid and the reflector of the apparatus of Fig. 1;

Fig. 1B` is a view in section of a spiked reflector that mayl be substituted for the conical or V- shaped-cross-section reflector of Figs. l and lA;

Fig.` 2 is an elevation view, partly in section of another embodiment of the invention in which a ribbon grid4 is utilized in place of the deep thinwalled grid of Fig. 1;-

Fig. 2A is a fragmentary view in section of the ribbon grid of Fig. 2;

Fig. 2B is av fragmentary view in section of a ilat reflector that may be utilized in place of the V-shaped reflector of Figs. 1 and 2;

Fig. 3 is` a fragmentary view in section of a modification of the resonator and secondaryemissive grid of the apparatus of Figs. 1 and 2;

Fig. 4 is an elevation View in section of another aspect of the invention in which a secondaryemissive grid and a reflector are disposed on each side of the resonator.

Referring to Fig. 1 andFig. 1A, there is shown an evacuated ultra-high-frequency discharge device i having a conventional pronged base 2 sealed to the lower portion of vacuum`- envelope 3, disposed within the lower portion of which is a cathode 8. Aiiixed, to the top end of the vacuum envelope 3 is a` metallic terminal cap 4 from which a. lead 5 extends toa. conical or V-shapedf cross-section reflector or reector electrode 6 Within vacuum envelope 3, the apex I of the V- shaped reflector 8 extending away from lead 5 and facing cathode 8. Thus, the configuration of reector electrode 6 is such as to provide it with a centrally projecting portion.

Intermediate cathode 8 and reflector 6 is a reentrant resonator 9 having an outer cylindrical wall I forming a portion of the vacuum envelope 3, and having an upper conductive end wall II and a lower conductive end wall I2. Positioned within and coaxial with resonator outer wall I is the resonator inner cylinder I3 which is rigidly fixed to lower end wall I2 and extends toward upper end wall II An entrance grid I4, aligned with cathode 8, is positioned at the end of inner cylinder I3 adjacent upper end wall II and an exit grid I5 is positioned within upper end wall I I and aligned with cathode 8 and entrance grid I4. Positioned within inner cylinder I3 and adjacent lower end wall I2 is accelerating grid I6. Cylinder IIS formed of insulating material surrounds exit grid I5 and is xed to and extends upwardly from upper end wall I I. Positioned at the upper end of cylinder I I8 and fixed thereto is grid I8 which is coated with efiicient secondary vemissive material I9.

Aiiixed to upper end of vacuum envelope 3 is V terminal cap 28 which is connected to secondary emissive grid I8 by lead 2I. Extending through outer resonator wall I!! is coaxial line terminal 22, which is utilized for extracting energy from resonator 9.

Connected between cathode 8 and resonator 9 l is potential source 23, whose positive and negative terminals are connected to resonator 9 and cathode 8, respectively, whereby an electron-acceleratng potential is provided between accelerating grid I6 and cathode 8. In order-to operate reflector 6 at a potential negative with respect to the cathode 8, variable voltage source 24 is connected therebetween. It comprises battery 25 and resistor 26 in shunt, resistor 26 hav- Cathode 8 is connected A' at a potential positive with respect to reflector 6,

variable voltage source 28 is provided. It comprises battery 29 and resistor 30 in shunt, resistor 30 having a variable tap 3 I. The negative terminal of battery 29 is connected tc reflector 6 and variable tap 3| of resistor 30 is connected to secondary-emissive grid I8 through terminal cap 20 vand lead 2 I.

In operation, electrons from cathode 8 are accelerated in the space between cathode 8 and accelerating grid I8 and are projected as a substantially constant-intensity beam through the gap between entrance grid I4 and exit grid I5 of resonator 9, where they are velocity-modulated by the oscillating eld in resonator 9. The velocity-modulated beam is bunched in the space between exit grid I5 and reflector 6, and, because of the negative potential on reflector 6, substantially all of the electrons are redirected towards the resonator 9.

As shown in Fig. 1A, the walls of the secondtheir initial paths, and a substantial portion of the reected electrons is intercepted by secondary-emissive grid I8 during their return toward resonator 9. Although a V-shaped reector vis used in this apparatus to cause the return paths of the electrons to be different from their initial paths, it is not intended that the invention be restricted to only that means for producing the desired results. Other means known to the art may be used, for example, another form of nonplanar reflector, such as the spiked reflector shown in Fig. 1B, which comprises a flat plate 32 and a spike 33 at the center of flat plate 32 and extending downward toward the secondary-emissive grid I8 and which may be substituted for reflector 6 of Fig. 1.

The returned electron beam is essentially a density-modulated or bunched beam, and the secondary electron beam, created by the impingement of the bunched primary beam on the secondary-emissive grid I8, is therefore also a density-modulated beam. Because of the potential difference between secondary-emissive grid I8 and exit grid I5 of resonator 9, the densitymodulated secondary beam is projected through exit grid I5 to give up energy to the oscillating field within resonator 9. The unintercepted portion of the density-modulated primary beam is also projected through exit grid I 5 and also gives up energy to the oscillating eld. Substantially all the electrons of the primary and secondary beams are collected on the inner walls of the resonator 9 and of the inner cylinder I3 after interaction with the oscillating eld within resonator 9. Inasmuch as the secondary to primary ratio of secondary-emissive material may be of the order of 25 or higher, it can be seen that the power output of the reflex Klystron is appreciably increased by the insertion of a secondaryemissive grid intermediate its resonator and reflector.

The operation of such a device is further improved by operating the secondary emissive grid at an appreciable potential diierence from the resonator, even though physically close to the resonator. By this operation of the device of Fig. 1, the transit time of the secondary electrons between the secondary-emissive grid I8 and the exit grid I5 is minimized and, therefore, debunching of the secondary beam is substantially prevented, resulting in an improvement in the efficiency of operation of the novel apparatus.

Referring to Figs. 2 and 2A, there is shown a modification of the apparatus of Fig. 1 which utilizes a flat ribbon secondary-ernissive grid I8 instead of the thin deep-wall grid shown in Fig. 1. Grid I8 is made up of a series of parallel iiat ribbons 34 positioned within and rigidly fastened to outer ring 35, the grid I8 being coated with ecient secondary emissive material I9. The operation of the apparatus of Fig. 2 is similar to the operation of the apparatus of Fig. 1. How-- ever, the major electron intercepting surface of grid I8 is now perpendicular to the axis of the electron beam, whereas the grid I8 of Fig. 1 has its major intercepting surface substantially parallel to the axis of the electron beam.

The operation ofthe apparatus of Fig. 2 is further improved by proper choice of potential difference between the grid I8 and resonator 9. It is known that the number of secondary electrons emitted from a secondary-emitting surface due to impingement of a primary beam varies with variation in primary impact energy over a limited range of primary impact energies, even though the density of the primary beam be constant. The electron beam emerging from reso-`v natorV 9 and` arrivingY at the secondary-emissivef grid I 8" is a velocity-modulated beam of substantially constant density. Inasmuch as the average velocityV of the electrons in the velocity,-

modulatedV beam at the secondary-emissive grid" I8' is a function of the accelerating voltage between the accelerating grid I6 and cathode 8 less the retarding voltage between exit grid I5 and secondary emissive grid I8', the average velocity of the velocity-modulated beam at4 grid I8 may be. adjusted to be within the above-mentioned limited range by adjustingV the potential .on grid I 3.V At this operating potential, that portion of the velocity-modulated electron beam' which is intercepted by the bottom faces oflthe.` flat ribbons 34' produces a density-modul'atedY secondary beam that is projected through the oscillating eld in resonator 9 by the accelerating voltage between secondary emissive grid I8 and exit grid I5 of resonator tou give up energy to the field. That portion of the velocitymodulated beam that is not intercepted by the; secondary-emissive grid ISl during initial traversal toward the reector becomes densitymodulated in the space between the secondaryemissive grid I8 and reector 5 and produces a second-density-modulated secondary beam when it impinges upon the secondary-emissive grid I8' during returnto the resonator 9. This action is similar to the action of the apparatus of Fig. 1 and, as inFig. l, the second density-modulated` secondary beam is projectedv through. the oscilllating field within resonatorv 9 to give up energy to the eld. Thus, it can be seen that, with proper choice of potential. difference between secondary-emissive grid I8 and exit grid I5, energy` is given` up to the oscillating eld by a densitymodulated secondary beam produced under` the, influence of a velocity-Inodulatedv primary beam of, substantially constant density in addition to, the energy given up by a density-modulated secondary beam produced under. the inuence. oi a density-modulated primary beam.

Aflat reflector S', as shown in Fig. 2B, may be utilized in place of theY V-shaped reilector IiY of' the apparatus of Fig. 2.

Fig. 3 shows a modification of, a portion. ofthe apparatus of Figs. 1 and 2inwhich the-resonator exit grid I5 is coated. with eicient secondaryemissive material as at I and is insulated from upper end wall II of resonator 9 by insulating ring 3S. As so constructed, theY single exit grid,l I5' may be utilized inplace of the'combinationof eXit grid and secondary-emissivegrid of the'l ap'- paratus of Figs.. l and 2.

Figa shows another aspectof the invention which a reector and. asecondary-emissive 'grid are` disposed on each side of the resonator' in order to eliminate the necessity' of a primary cathode during operation. The novel ultra-highfrequency electron discharge deviceY el includes toroi'dal cavity resonator 42, having upper andA lower opposing reentrant wall' portions i3 and- 44' in which are positioned grids i5 and 45, re'- spectively. Aligned with grid 115 and above resonator i2 is grid W which is. coated withsecondary-ernissive material and which is fixed to, but insulated from, resonator 42 by insulating ring e9. Beyond secondary-emissive grid 4'! is reflector or reectorelectrode 5G. Below resonator' 4'2 and aligned with grid 46 is' grid 5l, which islalso coated with secondary emissive material andi 6 is xed to, but insulated from, resonator 42 by insulating ring- 53. Positioned below secondary'-- emissive grid 5I is reflector or reiiectorA electrode 542 The upper portion-ofthe vacuum envelope'in` cludes a metallic cylinder 55 joined to upper Wall 133; coaxial with resonator d2, and sealed to a glass dome 56. The lower'portion of the vacuum envelope includes a metallic cylinder 51 joined: toV lowerwallv All, coaxial with resonator-62, and sealed to` glass domev 53. Brought out through upper glass dome 55 are leadsV 59 and to which are connected to' upper reflector 50 and upper secondary-emissive grid 41 respectively, and

brought' out through, lower glass dome 58 are' leads' 6I and; 52` which, are connected to lower reflectorv 54 and lower secondary-emissive grid;v lirespectively.

Resonator 42 is groundedat 63l and, for maintainingI secondary-emissive grids 4l and 5I at4v potentials negative with respect to resonator'liZ.` there are provided' voltage sources 64 and 65 whose positive terminals are grounded and'whose negative terminals are connected respectively to secondary-emissivey grids 4l and 5I through respective leads 65 and` 62. Secondary-emissive grids 4T and 5I 'are preferably operated at` the same potential. For maintaining reiiectors 50. and 54. negative with, respect to secondary-emissive grids Il and 5-.I andto resonator 42, there are provided voltage sources 56 andS'I whose positive terminals are grounded and whose negative. terminals areccnnected respectively to reectors and. 54. through respective leads 59 and 6I. ReflectorsV 5H. and 5.4" are. preferably also operatedat the samepotential..

Electron currentV iiow through resonator, 42' is. initiated by a helical starting filament or cathode 58 which ispositioned betweenthe lower reflector 54 andlower secondary-emissive gridY 5I- The helical starting filament 68 is coaxial with grids. 5.5 and 5I. and. its diameter is substantially. the same as their diameters. Connected to one. end.v of. helical larnent, 68. islead. 10 which, is. brought out through. lower glass dome 58 and which is connectedr to positive terminal. of battery lil. ConnectedY to the other end of helical filament. 68 is lead 69` which is also brought out. through lower. glass dome 58` andwhichisconnectedi to one, terminal of. a. threeterminal switch. 1I. ConnectedA to the second. terminal of` switch. 'il is the negative terminal of battery. ID and. connected to the third terminal is the negative terminal of battery I2 whose positive terminalY connected to lower secondary-emissive grid 5I through lead 62. In the closed position of switch 74 the threey terminals are-joined together electrically and, in. the open positioneach terminal, is=disconnectedfrom the other two. In the closed position, battery lll is connected across: filament igcausing electronv emission therefrom, andbattery: i2 is connected between filament G8 and lower secondary-emissive grid 5I, putting filament 58 at a potential intermediate the potentials of lower secondary-emissive grid5-I and lowerl reilector 5'4. in: the open position` of switch 1I. dlarnent t` is disconnected from bothk batteries lil: and 5.2" and hence no longer emits electrons and. is cutout of4 thezcircuit.V

In the closed; position of switch ll, the sub.- stantially constant intensity electron beam from starting dla-ment 68 issvelocity-modulated by the field in resonator 42. Part of the electron bearrr impinges upon: theupper secondary-emissve grid 41 and produces a secondary beam whose velocity is substantially unmodulated and which is redirected through resonator 42 by the accelerating voltage between upper secondary-emissive grid 41 and resonator 42.

Electrons passing through the upper secondary-emissive grid 41 are bunched to form a density-modulated beam which is redirected by upper reflector 58 toward secondary-emissive grid 41 and resonator 42. As more fully explained in connection with the apparatus of Figs. 1 and 2, part of the reflected density-modulated primary electron beam impinges upon secondary-emissive grid 46 and produces a density-modulated secondary beam that is projected through the oscillating field within resonator 42, to give up energy to the eld in addition to the energy given up to the field by the unintercepted portion of the reflected density-modulated primary beam.

The secondary beam whose velocity is unmodulated and which is obtained from upper second ary-emissive grid 41 traverses resonator 42 from upper resonator grid 45 to lower grid 46 and is velocity-modulated by the field in resonator 42. In a manner similar to that described in connection with the initial beam from filament 68, a secondary beam whose velocity is unmodulated is created by impingement of part of the velocity-modulated beam upon lower secondary-emissive grid 5I and is redirected through resonator 42 by the accelerating voltage between lower secondary-emissive grid 5l and resonator 42. Oscillations within resonator 42 are sustained by the action of the velocity-modulated beam in passing through the lower secondary-emissive grid 5|, and in becoming a density-modulated beam, as more fully explained in connection with the apparatus of Figs. l and 2. The secondary beam whose velocity is unmodulated and which is ob#- tained from grid 5| traverses resonator 42 from lower grid 46 to upper grid 45 and the process is repeated to maintain oscillations within resonator 42. After oscillations have been initiated, starting filament 68 is electrically removed from the circuit by opening switch 1|.

Thus, the present invention provides a reflex Klystron capable of producing large power output. In accordance with one aspect of the invention, the large power output is produced by the positioning of a secondary emissive grid intermediate the reector and the resonator of the reflex Klystron. The present invention further provides a novel cavity resonator electron discharge device in which the necessity of a continuously operating primary cathode is obviated.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention would be made without departing from the scope there#-l of, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. An ultra-high-frequency electron-discharge device comprising a resonator having a pair of aligned electron permeable walls, a cathode disposed on one side of said resonatorl and aligned with said walls, a reflector disposed on the other side of said resonator and a secondary-emissive grid structure intermediate said resonator an said reector.

2. An ultra-high-frequency electron discharge device comprising a resonator having a pair of aligned electron permeable walls, two secondaryemissive grids each disposed on an opposite side of said walls and aligned therewith, two reflector electrodes each disposed on an opposite side of said grids and aligned therewith, and a cathode disposed between one of said electrodes and an adjacent one of said grids.

3. An ultra-high-frequency electron-discharge device comprising means for producing an electron beam; means in said device for densitymodulating said electron beam including means along the path of said beam for velocity-modulating the electron beam and means electrically coupled to said beam including a reflector and defining a bunching space wherein the velocitymodulated beam is converted into a density modulated beam; and a secondary-,emissive electrode in the path of said electron beam.

4. A device as in claim 3 wherein said secondary-emissive electrode is a grid, said grid having a fiat ribbon construction.

' 5. A device as dened in claim 2, wherein said secondary-emissive electrode is a grid, said grid having a thin deep-wall construction.

6. An ultra-high-frequency electron-discharge device comprising means for producing an electron beam; means along the path of said beam for velocity-modulating the electron beam, a secondary-emissive electrode in the path of said velocity-modulated beam; and means beyond said secondary-emissive electrode including a reector and defining a bunching space wherein said velocity-modulated beam is converted into a density modulated beam.

7. A device as defined in claim 6 wherein said reector has a centrally-projecting portion, said portion extending substantially in the direction of said velocity-modulating means.

8. A device as dened in claim 6 wherein said velocity-modulating means includes a cavity resonator having a pair of grid means, one of said grid means providing said secondary-emissive electrode.

9. A device as defined in claim 6, further including a further secondary-emissive grid along the path of said beam and interposed between said electron beam producing means and said velocitymodulating means.

10. yA device as dened in claim 9, further including a further reiiector aligned with said beam path and positioned adjacent said beam producing means.

11. A device as defined in claim 6 wherein said beam producing means includes a helical filament.

12. A device as defined in claim 6, further including a further reflector and a further secondary emissive electrode, said further reflector and further electrode beam disposed adjacent said electron beam producing means.

13. A device as defined in claim l2, wherein said beam producing means includes a helical filament.

14. An ultra-high-frequency electron discharge device comprising means for producing an electron beam, a cavity resonator having a pair of grids, said grids being aligned along the path of said beam, said resonator effecting velocity modulation of said beam, and a reflector electrode spaced from said grids and aligned along said beam path, whereby said velocity-modulated beam is converted into a density-modulated beam, said grid closest to said electrode being electrically insulated from said resonator and being a secondary-emissive grid. y v

15. An ultra-high-frequency electron-'discharge device comprising means for producing an electron beam; means inV said device for densitymodulating said electron beam including means coupled to said beam for velocity-modulating the electron beam and means coupled to said beam including a reflector electrode and defining a bunching space for converting the velocity modulated beam into a density modulated beam; and a secondary-emissive grid located at a distance along the path of said density modulated portion of the beam.

16. Ultra-hlgh-frequency apparatus comprising means for producing a vbeam of electrons, means along the path of said electron beam for velocitymodulating said beam of electrons, a. non-planar reector electrode beyond said velocity-modulating means, and a secondary-emissive grid structure intermediate said reflector electrode and said velocitymodulating means.

DONALD R. HAMILTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

